In common-depth-point (CDP) stacking, signals, associated with a given CDP or reflection point but recorded at a number of source and receiver locations are composited ("stacked") either by field processors or in a playback center to produce a CDP stack. The signals are typically corrected for normal move out (NMO) and statics before stacking. CDP shooting produces redundant or "multifold" data from which a CDP stack can be made.
Arrays, that is, arrangements or patterns of sources and receivers, for taking multifold data for producing three-dimensional representations or profiles of seismic structure are known. One such array is the Broad-Line Profile Array represented in FIG. 1, labeled "Prior Art."
Referring to FIG. 1 in detail, FIG. 1 represents generally a portion of a Broad-Line Profile Array such as is known in the art and illustrates an areal recording geometry which will produce three-dimensional seimic coverage in 4-fold, if 96 trace records (8 cross-spreads of 12 receiver groups each) are recorded (only 4 cross-spreads are illustrated). Source locations are represented by the symbol "O", and receiver locations are represented by the symbol "X". An x,y coordinate system is provided in FIG. 1 and enables each source and receiver location to be represented ("indexed") by a pair of integers, i.e., an (x,y) doublet. Numbers in parentheses represent illustrative (x,y) doublets for certain source and receiver locations indicated in FIG. 1. The dashed lines P represent the boundaries of the Broad-line profile for which multifold data can be obtained using the illustrated recording and source geometry.
A common field method for taking multifold data for CDP stacking is the "roll-along" method, in which a plurality of sets of seismic shots are initiated at intervals, for example, in the broad line, and for each set of seismic shots, the set of seismic receivers is moved along ("rolled along"), for example, the broad line. The method of roll-along for the illustrative array of FIG. 1 is readily apparent. Twelve equally spaced shots can be made between the receiver cross-spreads at coordinates y=52 and y=100 and then, for example, the first receiver cross-spread at coordinate y=4 can be rolled forward to coordinate y=196 (not shown) before the next twelve equally spaced shots are taken between coordinates y=102 and continuing to coordinate y=146.
As indicated above, prior to CDP stacking or compositing, the signals from the receivers are typically corrected for NMO and statics. Corrections for statics in two-dimensional seismic recording can be obtained by solving the system of standard static correction equations characterized as follows: EQU T.sub.i,r =I.sub.i +R.sub.r +C.sub.d +(X.sub.i.sup.2.sub.,r M.sub.d) (A) EQU d=i+r
wherein i is the source location index; r is the group index; d is the depth index; t.sub.i,r is the observed two-way time for the seismic energy to travel the particular ray path from source point, i, to receiver group, r; I.sub.i is the initiation static-error term, R.sub.r is the receiver static error term, C.sub.d is the true two-way time which is desired for mapping, and the product X.sub.i.sup.2.sub.r M.sub.d is the NMO correction term.